A STUDY OF SELF-ALIGNED FORMATION OF C54 TI(SI1-YGEY)(2) TO P(+) AND N(+) SI0.7GE0.3 ALLOYS USING RAPID THERMAL ANNEALING

In this paper, solid state reactions of titanium with boron and phosph orus doped Si0.7Ge0.3 alloys have been investigated for application in a self-aligned germanosilicide process. Wet chemical etching of the g ermanosilicide with respect to unreacted Ti in a solution of 1:1:5 NH4 OH:H2O2:H2O has been investigated. Characterization was performed usin g four-point probe sheet resistance measurements, x-ray diffraction, c ross-sectional transmission electron microscopy, Nomarski optical imag ing, and scanning electron microscopy. The C54 Ti(Si1-yGey)(2) phase w as observed to form for reactions on both boron and phosphorus doped S i0.7Ge0.3 alloys. Grain structures of the C54 phases were found to be similar to grain structures of intrinsic alloy reactions with lateral grain dimensions on the order of 0.3 mu m. Resistivities of 22 mu Omeg a-m have been determined for the boron and phosphorus reactions. Altho ugh the germanosilicide phases were observed to etch slowly in 1:1:5 N H4OH:H2O2:H2O, which is conventionally used in the self-aligned titani um silicide process, the much higher etch rate of titanium nitride com pounds and unreacted Ti provided for a self-aligned germanosilicide pr ocess. A first anneal in a nitrogen ambient was found to be necessary to eliminate lateral silicidation over surrounding oxide during self-a ligned germanosilicide formation.